Relativistic 2-Body Kinematics        

The coding in catkin is essentially a translation into EXCEL of the fortran code relkin that was used at Daresbury Nuclear Structure Facility (with the correction of a minor bug that existed in relkin). As such, it is a little opaque to follow and to deduce the relevant formulae.

There are no doubt many places where the derivations of the relevant formulae can be found. One of the best and most straightforward that I have found (which also includes the non-relativistic formulations) was written by Carl Wheldon of the University of Birmingham, UK, and can be found at this link which is a file that I downloaded from an earlier version of Carl's site and on that version of the site there was also a code in c for calculating relativistic kinematics. I'm sure that you could get a copy by emailing him.

Another useful description that I found online is by an author in South Africa, in this file, and includes some python code. I originally found it here.

Wilton Catford
July 2019